Deep Sea Research (1953)最新文献

Dans les dépôts du nord-ouest de l'Océan Pacifique les diatomées se trouvent en abondance et en bonne conservation. Dans la coupe verticale des carottes l'on observe des modifications concernant la composition des diatomées et aussi de leurs quantités.

Les diatomées des époques glaciales se distinguent par une plus froide composition que la flore actuelle du nord du Pacifique. Pour la composition des diatomées de la dernière époque interglaciaire sont caracteristiques les espèces de la partie sud-boréale contrairement aux diatomées nord-boréales de la flore de plankton actuelle au nord du Pacifique.

Long waves, including Rossby waves and gravity waves, caused by a meteorological disturbance in an equatorial region are discussed by use of a theoretical model of a two-layer ocean. With the assumption that the frequency of wind stress variation is larger than the Coriolis' parameter, wave equations with a wind stress divergence as a forcing function are obtained. Forced waves initiated by a westward moving disturbance similar to the equatorial easterly waves indicate a resonance in the frequency range of gravity waves in a baroclinic mode and also in that of Rossby waves in both modes. The resonance in the gravity wave range seems to be responsible for the pronounced 4-day period oscillation detected at some Pacific islands.

Waves initiated by a sudden wind show no resonance, but interference between forced and free waves occurs near the period of resonance. The effect of a linear frictional force is shown to be more important in the Rossby wave range than in the gravity wave range. The effect of coasts is also studied and the proper oscillation of an ocean between two coasts is found to occur both in the Rossby wave range and gravity wave range.

When the frequency of the waves is decreased, the north-south distribution of the amplitudes must be modified owing to an increasing effect of the Coriolis' force in the sub-tropical zone of the wind. Analysis of the effect of the South Equatorial Current indicated that the response of sea-level has another resonant period in the intermediate range between Rossby waves and gravity waves. On the other hand, the current makes the resonant spectra of a period in Rossby waves so sharp that the resonance may be considered for practical purposes to vanish. The current also increases the amplitude of waves with periods of several days.

A treatment of stationary planetary flow patterns driven by source-sink distributions in a cylindrical tank (Stommel et al., 1958) is extended to predict flow patterns which might be expected under similar circumstances on a rotating sphere. Flow patterns are sketched for various source-sink distributions and meridional and zonal boundary conditions.

Gross and net primary production have been measured at bi-weekly intervals for 18 months in the North-western Sargasso Sea 15 miles SE. of Bermuda in 1500 fm of water. Ancillary data include temperature, salinity, phosphate, nitrite, nitrate, disolved oxygen, plant pigments, light penetration and incident radiation.

A seasonal cycle of production was observed with high levels in the winter and early spring, low levels in the later spring, summer and early fall. Gross production ranged from 0·13 to 2·00, averaging 0·44 g carbon assimilated/m²/day or 160 g C/m²/year. Net production ranged from 0·05 to 0·83 and averaged 0·20 g C/m²/day or 72 g C/m²/year.

Production was closely dependent upon vertical mixing, high levels occuring when the water was isothermal and mixed to or near the depth of the permanent thermocline (400 m), low levels being associated with the presence of a seasonal thermocline in the upper 100 m. Nutrient concentrations were extremely low (maxima of 1·8 μgAN/L and 0·16 μg AP/L as inorganic compounds in the upper 100 m) and showed little seasonal variability. Mixing and enrichment from the permanent thermocline is negligible, production being largely dependent upon the rapid re-cycling of nutrients within the upper 400 m.

The environmental factors controlling production which make this region differ from temperate or boreal waters, and which permit high production throughout the winter are: (1) low nutrient concentrations, (2) clear water, (3) relatively high incident radiation in winter, (4) a shallow winter mixed layer and (5) a rapid re-cycling of nutrients, possibly due to higher temperatures.

Current boundaries, the mixing zone of sea and river waters, and the thermocline may be identified by variations in the numbers of the microbial population. In the convergence zone of different water masses, boundary surfaces are formed where organic substances accumulate due to absorption phenomena or for other unknown reasons. As a consequence an increased number of micro-organisms occur there.

Microbiological studies in the Central Arctic showed that even slight variation in the stratification of the water could be detected by determining the abundance of the micro-organisms. The pronounced increase in the microbial population in the boundary layer of waters with only slight hydrographic differences makes it possible to utilize this phenomenon to identify weak, deep ocean currents.

Another method of the utilization of micro-organisms as hydrological indicators has been shown: investigation of areas of microbial forms with perculiar morphological characteristics makes it possible to determine the origin of water masses.

• 1.

  (1) A study of the vertical distribution of the numbers of heterotrophs was carried out at 56 stations in the Pacific Ocean along two parallel sections (174°W and 172°E from 37°N to 41 °S). The equatorial-tropical zone is distinguished by a relative abundance of heterotrophs assimilating only easily accessible organic matter.

• 2.

  (2) The equatorial-tropical waters are found at various subsurface levels in the sub-tropical areas. A very thick layer was observed in the northern hemisphere along 172°E where it was carried northwards by the Kuroshio current. Some strata of equatorial-tropical waters were also detected at considerable depths (6000–7000 m, 7500–9000 m) in the Kermadec trench.

• 3.

  (3) In the equatorial zone two layers of water, 375–550 m and 700–1800 m, were similar in their organic content to Arctic and Antarctic waters, these layers expanded considerably north and south from the equatorial zone. This circulation of waters from high latitudes across the equator also occurs in much deeper layers, judging from a layer of water with few heterotrophs observed near the equator at depths of 2500–4500 m.

• 1.

  (1) The microbiological investigations of the Indian Ocean water masses at 61 stations along the sections between Africa and the Antarctic, the Antarctic and Asia, showed that Antarctic waters are characterized by low concentrations of heterotrophs (which assimilate only easily accessible forms of organic substance), whereas the equatorial-tropical waters are characterized by high concentrations of these micro-organisms.

• 2.

  (2) The distribution of heterotrophs densities and individual bacterial species clearly indicate southerly currents carrying water from the tropical Indian Ocean south to the Antarctic coast and current flowing northward as far as the equator and the northern tropical zone.

• 3.

  (3) The microbiological data indicates a more complicated deep circulation in the Indian Ocean and in the adjacent parts of the Antartic Ocean than that suggested by Sverdrup, et al., (1956). The water masses flowing from the tropical zone to the Antartic coast were observed in the eastern half at depths of 25–75 m, 350–600 m, 1500–2500 m, and 2500–4000 m. In the tropical zone Antarctic water was found at 30–70 m, 100–300 m, 2500–3000 m, 3000–3500 m and in the equatorial zone at 1100–1500 m, 2000–2500 m, 2500–3000 m, 3000–3500 m.

An adaptation of the sound pinger designed by Edgerton to position an underwater camera for bottom photography has been used to monitor bottom coring operations with a Stetson corer. It is found that the pinger portrays the whole procedure in considerable detail, including the triggering of the corer for free-fall at the bottom. Cores have been taken successfully in water depths of 1912 and 2635 fathoms in the Ionian Sea.